In general, liquid crystal display devices are mounted in personal computers, wordprocessors, pinball machines, car navigation systems, compact TV sets, and the like. There have recently been great demands for liquid crystal display devices. However, liquid crystal display devices are expensive, and hence the demand for a reduction in cost has become increasingly higher.
A color filter as a component of a liquid crystal display device is formed by arranging pixels such as red (R), green (G), and blue (B) pixels on a transparent substrate. A black matrix for blocking light is arranged around each pixel to improve the display contrast.
As conventional color filter manufacturing methods, pigment dispersion, dyeing, electrodeposition, and printing are known.
In the pigment dispersion method, a pigment-dispersed photosensitive resin layer is formed on a substrate and patterned into a single-color pattern. This process is repeated three times for R, G, and B to form color filters.
In the dyeing method, a water-soluble polymer material as a dyeable material is formed on a glass substrate and patterned into a given shape by a photolithography process. The obtained pattern is dipped in a dye bath to obtain a colored pattern. This process is repeated three times for R, G, and B to form color filter layers.
In the electrodeposition method, a transparent electrode is patterned on a substrate, and the resultant structure is dipped in an electrodeposition coating fluid containing a pigment, resin, electrolyte, and the like to be colored in a single color by electrodeposition. This process is repeated three times for R, G, and B to form color filter layers. Finally, these layers are calcined.
In the print method, printing is performed three times by using materials obtained by dispersing pigments in a thermosetting resin to form R, G, and B coatings. Thereafter, the resin is cured.
These four methods have a common feature that the same process must be repeated three times to color layers in three colors, i.e., R, G, and B. Since a large number of processes are required, the yield decreases, resulting in an increase in cost and the like.
In the electrodeposition method, limitations are imposed on pattern shapes which can be formed. For this reason, this method cannot be applied to TFTs. In the print method, a pattern with a fine pitch cannot be formed because of poor resolution.
In order to eliminate these drawbacks, techniques of forming color filter patterns by discharging ink onto a glass substrate using ink-jet heads have been proposed.
In such an ink-jet method disclosed in, e.g., Japanese Patent Laid-Open No. 59-75205, inks containing coloring agents of three colors, i.e., R, G, and B, are discharged on a substrate by an ink-jet system, and the respective inks are dried to form colored image portions. In this ink-jet method, R, G, and B pixels can be formed at once, greatly simplifying the manufacturing process and greatly reducing the cost.
The first problem to be solved by the present invention will be described first. In these color filters, protective layers are often formed on colored (color) layers to smooth (flatten) the surfaces or protect the colored layers (colored portions). In this case, in order to sufficiently protect a colored layer, the thickness of a protective layer on the colored layer is required to be a predetermined value or more. In contrast to this, in consideration of the amount of material used, the protective layer is required to be thin. In a liquid crystal display device, in particular, a member called a spacer is often used to keep the thickness of the liquid crystal layer, sandwiched between the color filter and the counter substrate, constant. Assume that the protective layer is thick enough to sufficiently protect the colored layer. In this case, when a liquid crystal is injected into the space between the color filter and the counter substrate under a reduced pressure or the surface of the liquid crystal display device is pressed, the spacer sinks into the protective layer. This makes it impossible to keep the thickness of the liquid crystal layer constant. As described above, the first problem to be solved by the present invention is the problem of how to satisfy the contradictory requirements for the thickness of the protective layer.
The second problem to be solved by the present invention will be described next. Consider a method of manufacturing optical elements (display device panel including color filters, EL elements, and the like), in which recess portions surrounded by partition walls on a substrate are filled with ink containing a coloring agent, an evaporative liquid component, a holding component that holds the coloring agent upon evaporation of the liquid component, and the like by using an ink-jet system or the like, and the liquid component in the charged ink is then evaporated, thereby forming solid portions (colored portions) including the coloring agent and holding component left in the recess portions. In this method, as shown in FIGS. 13A and 13C which are sectional views of the substrate, the surfaces of the solid portions become uneven. Unless the shapes of the surfaces of solid portions are controlled, light may be undesirably refracted at the surfaces of the solid portions, or the attenuation amount of light in the solid portions may deviate from a predetermined amount depending on the position. Assume that a color filter used in a liquid crystal display device or the like is in the state shown in FIG. 13A. In this case, even if the coloring agent is uniformly held in the solid portions, the transmittance of rays of light transmitted through each recess portion varies locally depending on the distances from the bottom surface to the top surface of the solid portion. For this reason, if a color filter having uneven solid portion surfaces, like the one shown in FIG. 13A, is used, rays of light transmitted through the color filter are partly vignetted when the user obliquely sees the liquid crystal display device. As a consequence, for example, the user notices variations in color density.
FIGS. 13A and 13C show how the shapes of the surfaces of solid portions change, but do not indicate that these elements (display device panel) are always unsuitable as optical elements. Actually, for application to pinball machines, car navigation systems, compact TV sets, color filters and the like having planarities similar to those shown in FIGS. 13A and 13C suffice in many cases.
In T. Hasegawa, Y Ikuta, Y. Nonaka and N. Ishimaru, “Progress in Development of Color filters by Pigment Ink Jet Printing”, FMC3-4, p. 299–302, IDW'98 Proceedings of the Fifth International Display Workshops, the second illustration in FIG. 5 shows a state wherein the surface of a solid portion formed in a recess portion formed by partition walls on a substrate is almost planarized, with the distance from the bottom surface to the top surface of the solid portion being about 60% of the distance from the bottom portion to the top portion of each partition wall. However, this reference does not indicate that even if the distance from the bottom portion to the top portion of each partition wall differs from that shown in FIG. 5, the surface of each solid portion is almost planarized as long as the ratio of the mean distance from the bottom surface to the top surface of the solid portion formed in each recess portion formed by the partition walls on the substrate to the distance from the bottom portion to the top portion of each partition wall remains unchanged. This technique differs from the present invention in this point.
Japanese Patent Laid-Open No. 9-90342 discloses a technique of forming a color filter at a level lower than that of a light-shielding film and refers to the density of color in a colored area in association with a problem to be solved. However, this problem is ascribed to an insufficient amount of coloring agent supplied to an ink-receiving layer, and irrelevant to the technical problem to be solved by the present invention, i.e., the problem of planarization of the surfaces of solid portions. The prior art described above differs from the present invention in this point.
As described above, the second problem to be solved by the present invention is the problem of how to ensure good planarities of the surface of each solid portion (the surface of each colored portion) described above.